Recently, from the viewpoint of energy saving and environment protection, illumination apparatuses (for example, LED light bulbs) that use a light-emitting diode (hereinafter, also referred to as “LED”) as a light source are used as an alternative to incandescent light bulbs.
However, a conventional illumination apparatus that uses an LED as a light source emits light only in the forward direction, and cannot emit light in a wide direction like an incandescent light bulb. Therefore, unlike an incandescent light bulb, the conventional illumination apparatus cannot illuminate the inside of a room extensively using reflected light from a ceiling or wall surfaces.
In order to make the light distribution characteristics of such a conventional illumination apparatus that uses an LED as a light source close to the light distribution characteristics of an incandescent light bulb, technology has been proposed that controls the traveling direction of light emitted from the LED by the use of a light flux controlling member (for example, see PTL 1).
FIG. 1 is a cross-sectional view illustrating the configuration of illumination apparatus 10 described in PTL 1. As shown in FIG. 1, illumination apparatus 10 includes a plurality of LEDs 12 arranged on a substrate, and case 14 made of an optically transparent material and disposed so as to cover the LEDs 12. Case 14 is constituted by case body 14a in a cylindrical shape and cover section 14b formed in an inverted circular truncated cone shape. Case body 14a and cover section 14b are integrally formed in a single unit. A transflective film (half-mirror coating) 16 is formed on the inner face of cover section 14b. As indicated by arrows in FIG. 1, part of the light emitted from LEDs 12 passes through transflective film 16 and serves as light emitted in the forward direction (upward direction). Further, part of the light emitted from LEDs 12 is reflected by transflective film 16 and serves as light emitted in the lateral direction (horizontal direction) and in the backward direction (downward direction).
By controlling the traveling direction of light emitted from the LEDs using a light flux controlling member (case 14 in which semi-transflective film 16 is formed) having both optical transparency and optical reflectivity, in the manner described above, emitted light can be obtained not only in the forward direction, but also in the lateral direction and in the backward direction. Therefore, by using the light flux controlling member described in PTL 1, the light distribution characteristics of the illumination apparatus (LED light bulb) can be made close to the light distribution characteristics of an incandescent light bulb to a certain extent.